The present invention relates to a radio data communication apparatus, and a radio data communication method and system using the same, and more particularly, to radio data communication techniques which enable two radio data communication apparatuses, located at a distance too long to enable direct communication between them, to communicate with each other through at least one radio data communication apparatus which performs a relay function and exists between the two radio data communication apparatuses.
Conventionally, as disclosed in JP-A-3-250820 entitled "Local Area Network and Communication Network", radio communication ranges have been extended by additionally installed wired LAN (Local Area Network) for connecting base stations each other. However, the installation of wired LAN implies a problem that it needs additional expense and the system design requires extra labor and time. Generally, the installation of wired LAN requires a system design, construction, connectivity tests, and so on. In addition, once the network system is configured, it cannot be flexibly changed. Further, the cabling may often spoil good appearances. Thus, the construction of a wired LAN is not sometimes desirable in hired stores, offices with walls made of expensive materials (marble or the like), windows for serving customers, which must maintain good appearances, sales floors, and so on.
An example of the prior art for direct communications between radio terminals without intervention of a base station has been proposed in Mar. 7, 1994 issue of a magazine called "Nikkei Communications". In the scheme proposed in this example, however, communications available to each radio terminal is limited to a range in which radio waves sent from a transmitter directly reach a destination stations.
If radio waves from a transmitter do not directly reach a destination stations, a relay station is generally utilized for communications therebetween. The relay station may be searched through the following two techniques.
A first technique is ARP (Address Resolution Protocol) which is used for address resolution for a protocol called TCP/IP. This technique, however, is intended to search for a physical address of a destination station but not for an address sequence of relay stations. Neither one performs chain extension of broadcast in consideration of a radio wave range (zone) which is particular in the radio data communication network. For reference, ARP is described in RFC826 "An Ethernet Address Resolution Protocol" published from Internet Society.
A second technique is source routing in IEEE802.5 in which, however, a relaying system is limited to a particular bridge. Further, every station does not perform a chain extension of broadcasts in consideration of a radio wave reachable range (zone) which is particular in the radio data communication network. In the source routing, an alternative route must be previously prepared for a failure of the bridge. Otherwise, a bypass route cannot be ensured for the communications in case a failure occurs.
In the prior art as described above, an extension of radio communication area requires the installation of wired LAN which is sometimes severely restricted in terms of location, time and cost.
Also, as the route of communication is fixed, the prior art for the communication system has other problems that its resistance to failures for the cable and extra communication devices is lower and controlling distribution of traffic loads is difficult.